Optical fiber transmission systems are beginning to achieve their great potential for the rapid transmission of vast amounts of information. In essence, an optical transmission system comprises an optical signal source and an optical fiber transmission path for carrying the optical signals to a receiver for demodulating the information the signals carry. Increasingly the optical signals are wavelength division multiplexed signals (WDM or DWDM signals) comprising a plurality of distinct wavelength signal channels. In each channel information is typically transmitted as a sequence of optical pulses.
Polarization mode dispersion compensators are potentially important components of optical transmission systems. Polarization mode dispersion (PMD) occurs when different orthogonal polarization components of a signal are subject to different propagation delays. Imperfections in fibers and optical components can produce differing delays in the polarization components. These differing delays can distort the shape of transmitted signal pulses.
PMD is of increasing concern at higher bit rates, particularly at 40 Gb/s and above. Moreover, since PMD can vary with frequency, it is increasingly difficult to compensate systems that transmit optical signals over a wider range of frequencies. Accordingly there is a need for an optical fiber transmission system with improved PMD compensation.